3. INTRODUCTION
DORMANCY
During the developmental cycle of the plant, at
some phase certain structures like buds, tubers,
seeds, go though a period of temporary
suspension of growth activity or slow down for a
period of time or deep sleep, such a state is called
Dormancy.
This minimizes metabolic activity and therefore
helps an organism to conserve energy.
Dormant = not active or growing but able to3
become active later.
4. Seed Dormancy
It is the incapacity of fully
developed, mature, viable seed to
germinate even under favourable
conditions.
In such cases, the completely dry
ripe seed is physiologically inactive
and is said to be in a resting stage.
The seed is called dormant and the
phenomenon is termed Dormancy
4
5. The main reason behind this condition is
that they require a period of rest before
being capable of germination.
This Conditions may vary from days to
months and even years.
5
7. TYPES OF DORMANCY
1) Imposed dormancy or quiescence
The dormancy due to unfavourable
environmental conditions is called
imposed dormancy or quiescence.
2) Innate dormancy or rest
The dormancy due to conditions within
the dormant plant or organ is called
innate dormancy or rest.
It is a condition in which germination or6
growth fails to occur even though the
external environmental conditions are
favourable.
8. During the entire process, there may be
following three phases of dormancy :
1) Pre-dormancy or early rest :
During these phase, the dormant organ has
capacity to resume growth by various
treatments i.e., capacity of germination or
growth is not completely lost. It is called
predormancy.
2) Full dormancy or mid rest :
When a seed or organ becomes completely
dormant and germination or growth
cannot be induced by changes
environmental conditions, it is called full
dormancy or mid
7
rest.
9. 3) Post dormancy or after rest :
When a or organ gradually
emerges
dormant seed
from full
germination or growth can be induced
dormancy and in it the
by
changing enviornmental conditions, it is called
post-dormancy or after rest.
10. Causes of Seed Dormancy
1. Seed coat: The seed coat is hard and
impermeable and prevents the entry of water
and oxygen.
2. Growth inhibitors: Some seeds may
contain chemical growth inhibitors like
abscisic acid (ABA), coumarin, phenolic
acids and short chain fatty acids in the
embryo. Endosperm or other tissues may
also prevent germination.
11. 3. Specific light requirement: In certain seeds,
dormancy can be broken by exposing them to
optimum light (after seeds have been soaked)
while in some others, seeds remain dormant as
long as they are exposed to light.
4. Optimum temperature: Generally the seeds
require a low temperature before germination. It
brings about an increase in the gibberellin level.
5. Immaturity of the embryo: At the time of
dispersal, some seeds are structurally immature
and the embryo is unable to synthesize
gibberellic
acid.
12. METHOD TO BREAK SEED DORMANCY
Seed coat dormancy can be overcome by
weakening the seed coat in a number of ways in
various seeds:
1. In some seeds, the seed coat is softened by
soaking in water.
2. Hard seed coat can also be softened by certain
enzymes present in the digestive tract of birds
and animals
3. At times scratching of seed coat called
scarification or artificial removal of testa or
pricking it with a pin also helps to break the seed
dormancy.
4. Certain seed coats can be broken down by soil
microorganisms also.
13. METHOD TO BREAK SEED DORMANCY
To break seed dormancy by chemical growth
inhibitors, their concentration has to be
lowered.
It can be achieved by:
1. Exposing the seeds to alternating
temperature, chilling, light, placement in
running water, treatment of hydrated seeds
with oxygen, nitrates, nitrites and thiourea.
2. Treatment with certain hormones or
chemicals
like gibberellins, cytokinins and ethylene
14. ADVANTAGES OF SEED DORMANCY
1. It enables the seed to germinate only under
favorable conditions, e.g. if the seeds
dispersed
in summer germinate immediately the
seedlings
cannot survive the following cold season.
2. It allows seeds to survive through
unfavorable conditions and germinate at the
onset of favorable season.
3. The dormant seeds can be stored for a long
time and the seed dormancy can be broken by
giving artificial conditions
15. ASSIGNMENT
1. Define Seed Dormancy?
2. Mention five (5) causes of Seed
Dormancy?
3. Discuss three (3) advantages of
Seed Dormancy?
4. Discuss four (4) ways to break
seed dormancy?
